Customized clear sky to calculate reflected radiation


I found that the ASHRAE clear sky always include the diffuse radiation. I wanted to use customized clear sky which only includes the direct normal radiation, not diffuse horizontal radiation.

Thus, I changed the as below.

(original) diff_horiz = 0.17 * dir_norm * math.sin(math.radians(alt))
(reviesed) diff_horiz = 0

But, when I do simulation with this revised,
the result doesn’t include “sky + diffuse values”.
And the total values doesn’t change although I change the reflectivity of louvers.

How can I make the customized clear sky working with the reflectivity of material?

Thanks for your answers.

Best regards, (59.0 KB) (8.1 KB)

Dear all,

I want to ask this simple question to all of you.

So far, I thought that the radiance-opaque material can reflect the direct radiation.
But, it seems that the radiance-opaque material only can reflect the diffuse radiation.
Is it true?

Thanks for your comments…

Best regards,

Jaeman PARK

Opaque-materials, as characterized in Honeybee, are Radiance plastic materials. For the format defined in that link ( mod plastic id 0 0 5 red green blue spec rough), Honeybee-opaque materials usually only assign values for red, green and blue.

As far as I remember, only the diffuse channels are set by default in Honeybee. You can tweak the other values to get a more reflecting material. Alstan Jakubiec and his students have created a database of architectural surfaces in Radiance format. Those can be accessed here:
If you need a completely specular surface, mirror might be the best option (while keeping things simple).
In terms of what is possible with respect to modeling shiny surfaces n Honeybee(Radiance), here is an interesting example from a few decades ago: NIST BRDF Measurements Rendered using Radiance (Check out the rendered images for the car in the bottom!)


Thanks Sarith,

I think that the difference between Radiance plastic and mirror materials is not that much. Because I can input specularity of plastic material as Zero. Is it right?
You said that “only the diffuse channels are set by default in Honeybee”. Then I have problems because I don’t have experiences about using pure Radiance. That’s why many people including me use Honeybee(plus) or something to do simulations with easy interface.
I can try to edit .py script if possible. My goal is

  1. Making clear sky with diffuse radiation Zero ; I made it.
  2. Doing daily radiation simulation on facade with louvers; OK
  3. Testing different reflectivity of louvers, to expect that direct radiation will be reflected on the louvers; it doesnt’ work.

Do you think that no.3 is impossible on Honeybee Plus?

Thanks for your answers.

Best regards,
Jaeman PARK

Hi Jaeman, it is possible. What kind of material are you working with? Is it a metallic finish or a really shiny plastic type surface?

hi @sarith,

Speaking of radiation, are the complexity settings for radiance in HB+ as much effective for radiation as for daylighting? The simulation times seem to be higher and accuracy hard to assess.


Hi @OlivierDambron, can you share a sample project folder with me (i.e. one where the Radiance files have been written out)? I would like to peek inside the commands and see what is going on. The settings for radiation are assigned upstream in grasshopper and I dont have access to a stable Rhino installation right now.


Just a quick thought about what could be happening: it’s possible that the ambient accuracy (aa) and ambient resolution (ar) are not set high enough to resolve the louvers (I know that this has happened to me in the past when modeling small geometries). An image based rendering with the same settings will give some insight into this. Also, depending on how reflective those louvers get, you probably also want to boost up the ab. For example, if the louvers are really reflective (like 80%), you can still get a significant amount of light off the 5th or 6th bounce.

Hi @chris, the settings related to ambient accuracy and ambient resolution do not apply to rcontrib, the tool that we use for annual calculations in Honeybee[+]. There are actually no ambient caching related optimizations possible with rcontrib and the only way to increase the number of rays traced is to increase the value of ambient divisions and correspondingly decrease limit weight -lw.

Hi Sarith,

I attached my GH file.
You said that it’s possible to reflect the direct radiation on the louvers.

Dear all,

It’ll be helpful if you upload the example file for the answer.


Best regards, (73.4 KB)

Hi @jamparc, sorry for the late reply. I dont have access to a stable Gh installation right now. Can you write out the Radiance files and share the Radiance folder instead?


Hi @sarith,

Sorry for my late reply, too. And I couldn’t understand your request clearly.

I attached the .zip files from the C:\ladybug folder.
Each simulation was done with different

And, also attached the file exported by HBToRad component. But I feel that this file cannot explain my situation. HB_objects (635 Bytes) (240.4 KB) (401.3 KB) (8.1 KB) (8.1 KB)

Best regards,
Jaeman PARK